On the stability of a coupled ocean atmosphere system in the presence of wave-CISK

Selvarajan, Sudha and Goswami, BN
(1992)
On the stability of a coupled ocean atmosphere system in the presence of wave-CISK.
In: Proceedings of the Indian Academy of Sciences, Earth and Planetary Sciences, 101
(2).
pp. 153-176.

Abstract

The stability of a simple coupled ocean-atmosphere system similar to the one studied by Hirst with general ocean thermodynamics is investigated in which the atmospheric heating is determined by sea surface temperature anomalies as well as the convergence feedback (low level moisture convergence by the waves themselves). It is shown that the unstable coupled mode found by Hirst (UH mode) is profoundly modified by the convergence feedback. The feedback increases the unstable range of the UH mode and can increase its growth rate several folds. The maximally growing UH mode can become westward propagating for certain strength of convergence feedback. If the convergence feedback strength exceeds a critical value, several new unstable intraseasonal mode are also introduced. These modes are basically `advective' modes. For relatively weak strengths of the convergence feedback the growth rates of these modes are smaller than that of the UH mode. As the atmosphere approaches `moist neutral' state, the growth rates of these modes could become comparable or even larger than that of the UH mode. It is argued that these results explain why the El Nino and Southern Oscillation signal is clear in the eastern Pacific but not so in the western Pacific.